HOXIE (AP) — An important highway in northeast Arkansas could stay closed into next week as crews clean up the wreckage left from a head-on train collision, a highway official said Wednesday.

Two railroad workers were killed and two others were injured when the Union Pacific freight trains crashed.

Railcars tumbled across the area near Hoxie and forced the closure of U.S. 67 so crews could clean up the mess.

Arkansas Highway and Transportation Department spokesman Randy Ort said the highway would probably reopen this weekend but could be closed into Monday.

"The railroad's got quite a cleanup going, Ort said.

The Union Pacific rail line runs parallel to the highway, where traffic is being detoured.

National Transportation Safety Board spokesman Terry Williams said the agency would have more information available in a week or two when a written report is completed.

Investigators at the scene want to find a data recorder from a signal that was plowed under by the errant railcars. The signal would have given a final instruction to the southbound train and could reveal whether it was told to stop or go.

Union Pacific is among railroads under a congressional deadline to put a new safety system in place that would prevent the worst collisions and derailments.

Congress ordered the industry to have the system in place by the end of next year, but industry representatives said the system would only be 20 percent deployed by the deadline. Known as positive train control, the safety system uses GPS, wireless radio and computers to help prevent human error.

Bob Chipkevich, who served as the NTSB's director of Railroad, Pipeline and Hazardous Materials Investigations in Washington, D.C., for nine years and now works as a consultant, said the system was installed years ago along the northeast corridor.

"Once GPS was developed and perfected, it became useful on a national basis. You don't need to install transponders all along the track," Chipkevich said.

The system keeps track of where trains are and how fast they are going as a way to head off collisions and speed-related derailments.

"It (the positive train control system) knows the speed limit. Data is fed into a computer for traffic control signals, what the speed is for a zone, if there is a caution and then a stop," he said.

The system factors in the length and weight of the train, whether it is on an uphill or downhill slope and determines whether the train needs to brake.

"The technology is there. It has existed for several years," Chipkevich said.